To find out how many puzzles one student completed, you can divide the total number of puzzles by the number of students.
So, you can calculate it as follows:
\[ \text{Puzzles per student} = \frac{\text{Total puzzles}}{\text{Number of students}} = \frac{80}{15} \]
Calculating this gives:
\[ \frac{80}{15} \approx 5.3333 \]
Rounding 5.3333 to the nearest tenth gives you 5.3.
So, the answer is 5.3.